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Little critters, big energy

ORNL team receives $2 million to study use of microbial
electrolysis in biorefineries

Scientists are using one of Earth's smallest creatures to solve some of the government's biggest bioenergy problems.

For the next three years, a $2.1 million grant will allow ORNL researchers to use a process called microbial electrolysis to transform plant biomass into hydrogen to produce energy-rich biofuel for use in combustion engines.

With conventional technology, industries convert biomass into bio-oil—a corrosive substance that turns into biofuel after it's treated with natural gas. This treatment provides hydrogen atoms that can deoxygenate bio-oils, but the process also emits a significant amount of carbon dioxide.

The US Department of Energy has given the laboratory the three-year grant to address this environmental issue and boost the hydrogen and carbon efficiency of biofuel production.

"We think we can solve the problem by using live microbes instead of natural gas and chemical catalysts to create biofuels," says project leader Abhijeet Borole of ORNL's Biosciences Division. "We know that microbes can convert organic compounds into hydrogen gas, but the process doesn't yet run at a high enough rate or with enough efficiency to work in a huge reactor where thousands of gallons of the bio-oil aqueous phase need to be treated every day."

Microbial electrolysis cells act like batteries in reverse. Instead of consuming fuel, they actually help create it.

The process requires a small energy input, but the majority of energy is produced by electrogenic microbes—a type of bacteria that generates electricity while dining on organic compounds. These microbes eat the bio-oil's organic acids and produce an electrical current capable of converting the corrosive compounds in bio-oil and water into hydrogen.

"These microbes can reduce the energy normally needed to hydrolyze water by up to 70 percent while consuming the corrosive organic compounds," Borole says.

It's a healthy exchange. Scientists provide the microbes with food, and the microbes, in turn, produce hydrogen to make biofuels that can be used for transportation.

Borole envisions thousands of microbial electrolysis cells configured as stacks alongside other biorefinery unit operations. Each cell will contain electrodes coated with 50 to 100 layers of electricity-generating microbes.

For this process to work efficiently, ORNL's team must build a microbial community that can digest the organic compounds found in the aqueous phase of bio-oils and create a system that can harness the electrical currents produced.

ORNL's team is collaborating with researchers at Georgia Tech and the University of Tennessee to solve these problems and improve other aspects of the biofuel production process. They are also working together to develop membrane separators that can recycle water in biorefineries, improve the process that separates water and oil emulsions, optimize microbial electrolysis and identify the organic compounds in bio-oils available for microbial breakdown. The team includes scientists from a wide range of disciplines—chemistry, biology, microbiology, environmental science and engineering.

"We are working together to develop the microbial electrolysis process and other supporting processes so that eventually microbes can help mass-produce hydrogen to produce biofuel," Borole says. "There is a difference between scientific and technological progress. We want to see if we can bridge that gap." — Jennifer Brouner